SPECIAL ISSUE ON TRANS-DISCIPLINARY APPROACHES TO CLIMATE CHANGE

Challenges of using air conditioning in an increasingly hot climate

Karin Lundgren-Kownacki1 & Elisabeth Dalholm Hornyanszky1 & Tuan Anh Chu2& Johanna Alkan Olsson3

& Per Becker4

Received: 8 July 2016 /Revised: 17 October 2017 /Accepted: 11 December 2017 /Published online: 30 December 2017# The Author(s) 2017. This article is an open access publication

AbstractAt present, air conditioning (AC) is the most effective means for the cooling of indoor space. However, its increased global use isproblematic for various reasons. This paper explores the challenges linked to increased AC use and discusses more sustainablealternatives. A literature review was conducted applying a transdisciplinary approach. It was further complemented by examplesfrom cities in hot climates. To analyse the findings, an analytical framework was developed which considers four societallevels—individual, community, city, and national. The main challenges identified from the literature review are as follows:environmental, organisational, socio-economical, biophysical and behavioural. The paper also identifies several measures thatcould be taken to reduce the fast growth of AC use. However, due to the complex nature of the problem, there is no single solutionto provide sustainable cooling. Alternative solutions were categorised in three broad categories: climate-sensitive urban planningand building design, alternative cooling technologies, and climate-sensitive attitudes and behaviour. The main findings concernthe problems arising from leaving the responsibility to come up with cooling solutions entirely to the individual, and howdifferent societal levels can work towards more sustainable cooling options. It is concluded that there is a need for a more holisticview both when it comes to combining various solutions as well as involving various levels in society.

Keywords Air conditioning . Climate change . Urban areas . Sustainability . Transdisciplinary

Introduction

Increasing heat exposure levels are one of the most certaineffects of climate change (IPCC 2014) and there is strongevidence of negative health impacts of environmental heat(e.g. Forzieri et al. (2017), Gasparrini et al. (2015), Aströmet al. (2015), and Canouï-Poitrine et al. (2005)). Heat exposureis particularly problematic in tropical and subtropical climates(Kjellstrom et al. 2009), although there is a significantheatwave-related mortality risk in warmer temperate climatesas well (e.g. Poumadère et al. (2005), Patz et al. (2005), and

Kaiser et al. (2007)). Heat exposure is particularly problematicin large cities due to what is referred to as the urban heat island(UHI) effect (Oke 1982; Patz et al. 2005). In addition, areaswith already and increasingly hot climates are the areas withhigh urbanisation rates and population growth (UnitedNations 2015). This puts escalating numbers of people at risk.

Air conditioning (AC) is promoted as an effective solution toreduce heat stress and protect from heat exposure by providingindoor thermal comfort to avoid heat-related health problems(e.g. Whitman et al. (1997), Chestnut et al. (1998), Davis et al.(2003), Barnett (2007), Bouchama et al. 2007, and Andersonand Bell (2009)). Although there are several good reasons forincreased AC use, it is important to question the material, dis-cursive and social aspects of AC.O’Neill (2003) described prob-lems related to the widespread adoption of AC more than adecade ago, and argues against the non-critical approach foundin some of the public health and epidemiological research fieldsthat promote AC as the most effective solution (e.g. Whitmanet al. (1997), Chestnut et al. (1998), Davis et al. (2003), Barnett(2007), Bouchama et al. (2007), and Anderson and Bell (2009)).

This review paper rests on the premise that there are addi-tional perspectives available than that of solely adopting a

* Karin Lundgren-Kownackikarin.lundgren_kownacki@design.lth.se

1 Department of Design Sciences, Lund University, 22100 Lund, Sweden

2 Department of Architecture, Lund University, Lund, Sweden3 Centre for Environment and Climate Research, Lund University,

Lund, Sweden4 Division of Risk Management and Societal Safety, Lund University,

Lund, Sweden

International Journal of Biometeorology (2018) 62:401–412https://doi.org/10.1007/s00484-017-1493-z

technological solution such as AC. Such an updated andexpanded overview is particularly pertinent in the light ofour increasing cognisance of climate change and the currentescalation of AC use. Dahl (2013) anticipates a tenfold in-crease in energy demand for cooling by 2050 if the use ofAC continues to follow current trends. This increase is expect-ed to be concentrated to the fast growing and dense cities inareas with tropical and subtropical climates (e.g. Parkpoomand Harrison (2008)).

The purpose of this review paper is to explore challengeslinked to increased AC use as well as more sustainable coolingoptions in order to inform future approaches to handling urbanheat. To meet this purpose, the paper sets out to answer thefollowing two research questions:

– What are the challenges of increased AC use found in thescientific literature?

– What are the possible alternative solutions to AC usefound in the scientific literature?

We also illustrate the findings from the literature reviewwith examples from urban areas in hot climates.

Analytical framework and methodology

An analytical framework consisting of four parts guided theliterature review (see Fig. 1). Inspired by studies on climatevulnerability, we recognised that society is influenced by a setof global processes of change, such as climate change, popula-tion growth, urbanisation, increasing inequality, globalisation,and increasing complexity (Becker 2014). We also recognisedthat society adapts proactively or reactively to the resultingchallenges (Adger 2006; Anderson and Woodrow 1989;Kelly and Adger 2000; O’Brien et al. 2007). Inspired by

multi-level governance methodology, we assumed that chal-lenges as well as solutions may be produced or addressed atdifferent levels in society. Consequently, we added a spatialdimension to the challenges and structured the discussion ac-cording to the level of societal organisation the solution ad-dresses (Fig. 1). Particular attention was given to identifyingcircular relationships, in which one challenge is reinforcedthrough the feedback from another.

A literature review of peer-reviewed papers explored thechallenges of AC use. A literature review is a suitable meth-odology for the purpose of this paper because it can be used tocreate an overview of what is known in a specific area, and canadd detail and depth to a specific problem (Bryman 2008).The development of search terms for the literature searchwas carried out in a transdisciplinary setting to ensure a broadidentification of challenges and alternative solutions, includ-ing environment and sustainability science, architecture andurban planning, social sciences, health, risk management, andthermal environment research. The literature review involveda three-step process:

Step one included the following: (i) the identification ofsearch terms and alternatives to increased AC use, (ii) data-base searches, (iii) identification of challenges, and (iv)categorisation of challenges in the framework. Step two com-prised the use of the search terms and categorisations to inves-tigate what the current literature says about the five identifiedchallenges of increased AC use to handle urban heat: environ-mental, organisational, socioeconomic, biophysical, and be-havioural. In step three, alternative solutions were identifiedthrough a second literature search, also of peer-reviewed pa-pers. Solutions were categorised into three broad categories:urban planning and building design, alternative cooling tech-nologies, and attitudes and behaviour. These categories relateto the different societal levels where solutions can be

Fig. 1 Analytical frameworkvisualising the relation betweenglobal processes of change,challenges related to AC use,solutions, and societal levelswhere solutions are identified

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implemented (Fig. 1). This is a novel approach to discussingthe role of cooling in a hot climate compared to those providedby the narrower-scope literature currently available.

Challenges with air conditioning

This part of the literature review is structured according to thefive categories of challenges (Fig. 1). The first three catego-ries—environmental, organisational, and socioeconomic—aresystemic. The last two—biophysical and behavioural—areindividual but intimately related to the societal context andsocioeconomic situation of individuals.

Environmental challenges

The adoption of AC increases the use of electricity or energy.It is currently estimated that the world consumes about onetrillion kilowatt hours (kWh) of electricity for AC annually,more than twice the total energy usage of Africa for all pur-poses (Dahl 2013). The modelling results of Isaac and vanVuuren (2009) show that world energy demand for AC willincrease rapidly in the twenty-first century. The increase in themedian scenario for AC-induced growth in electricity use isfrom close to 300 TWh in year 2000, to about 4000 TWh in2050 and more than 10,000 TWh in 2100 (Isaac and vanVuuren 2009). Widespread AC use places a heavy burdenon the electricity distribution system and increases the riskfor electricity power cuts (Parkpoom and Harrison 2008).IIASA's Global Energy Assessment report (2012) identifiesthat the choices of cooling technology will prove increasinglyimportant for the development of energy use. These choicesare already causing problems in many parts of the world dueto increased electricity use (IIASA 2012).

As the use of AC is resource and energy intensive, it hasconsequently a potential negative impact on both climatechange and the environment in general (Brager et al. 2015).Its impacts on climate change depend on the type of energysource used to produce the cooling. AC significantly increaseselectricity use (Valor et al. 2001; Crowley and Joutz 2003;Parkpoom and Harrison 2008; Izquierdo et al. 2011; Liuet al. 2011; Rosenthal 2012; Lundgren and Kjellstrom2013). AC also contributes to the UHI effect and directlyaffects outdoor thermal comfort on streets through heat ejec-tion (Yahia and Johansson 2013). Elevated urban tempera-tures, including UHIs, can increase the magnitude and dura-tion of heat waves and cause additional night-time electricityconsumption from AC (Kovats and Akhtar 2008). Climatechange will create higher outdoor heat exposure levels(IPCC 2014) and if developments follow the current trajectoryboth in relation to expected temperature rises and the speed ofAC adoption, there will be an increased use of AC in urbanareas especially in the tropics and subtropics. This will create a

negative feedback loop related to energy use and to the UHIeffect.

One example where the use of AC is growing rapidly is inSouth and Southeast Asia (Isaac and van Vuuren 2009). In2010, the Vietnamese building sector accounted for 20 to24% of the total national energy use, which is expected toincrease significantly, especially due to increased AC use(Nguyen et al. 2011; Le Phan and Yoshino 2010). From1998 to 2008, the nationwide electricity consumption in-creased by 400%, in which the electricity consumption foradministration and household accounts made up the largestproportion (Nam et al. 2015). This development is mostlydriven by income growth and poor building design, but alsoby increasing heat exposure due to urban growth. It is expect-ed that Hanoians will continue to rely solely on AC forcooling, since it is among the fastest growing AC marketsglobally and the general level of awareness fails to addressproblems associated with AC usage (Pham et al. 2014).Furthermore, the current situation with rising temperatures inHanoi has undermined all attempts to reduce energy consump-tion, especially for cooling purposes. In fact, a heatwave in2015 showed a record high 30% increase in maximum use ofelectricity in Hanoi (Lao Dong News 2015). A number ofofficial statements from Vietnam Electricity have indicatedthat the need for cooling accounted for the largest part of theincrease.

Organisational challenges

The organisational challenges are related to how we chose andorganise supportive services and howwe organise and design thedevelopment of our cities. When people grow increasingly de-pendent on AC for cooling their homes, they are not only con-tributing to increased urban temperatures due to outlet of hot air,but they are also increasing their vulnerability. Building housesand communities that are dependent on AC for coping with heatplaces them at the mercy of electric power cuts, which maybecome more common when the use of AC intensifies the stresson the electric distribution system (Parkpoom and Harrison2008). Increasing dependencies between societal systems, suchas systems for electricity production and distribution and onesthat provide thermal comfort, are well-known contributors toincreased risk and vulnerability, as the growing complexity in-creases the likelihood that two or more failures interact in waysthat are difficult to anticipate (Perrow 2008). A consequence ofsuch dependencies is that it becomes gradually more difficult tooverview and manage the multiple layers of risk, as well as theconsequences of actual events and decisions to handle them,since effects can spread across these chains of dependenciesthroughout society (Rasmussen and Svedung 2000).

Being dependent on electricity for cooling is, in otherwords, making people dependent not only on the functioningof the electricity distribution system as such, but also on all

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other connected systems. For instance, an increased need forelectricity also creates a dependency on global oil and coalprices or on political decisions regarding water resource man-agement, since fossil fuels and hydropower stations are themain energy sources in many countries. In addition, such asociety becomes more vulnerable to cyclones and other haz-ards that may cause major destruction and prolonged powercuts (e.g. Han et al. (2009)). Becoming more dependent onelectricity for cooling homes thus locks people into a web ofdependencies that ultimately increase their vulnerability toheat.

At the heart of this problem lay, in other words, dependen-cies through which interconnected effects can cascade andreinforce each other in society (Rinaldi et al. 2001; Little2002). Such dependencies and slowly evolving increases insocietal complexity have been referred to as Bcreepingdependencies^ (Hills 2005), which accumulate and eventuallyreach a threshold where we lose the oversight and much of ourability to manage risks in our societies.

There are many reasons why societies have developed intohighly complex structures but they will not be discussed inthis paper. However, according to the literature review, it isobvious that current and previous trends in urban developmentand design are influencing and worsening the dependency onAC. One of them is the globalisation of urban developmentand housing ideals/trends, resulting in urban designs andbuildings that abandon vernacular building tradition and lackthe knowledge of how to adapt to the local climate that hasdeveloped over centuries.

This is the case in Hanoi where the Bnew urban areas^(NUAs) is an urban planning model that has been promotedsince the turn of the century to meet the increasing demand forhousing (Tran 2008). These master-planned developments atthe city’s peripheries are more spread out, which creates adifferent urban space from the very dense and compact olderparts of Hanoi’s inner city. The high-rise apartment blocks anddetached houses are built to rely entirely on AC and littleattention is paid to build in an energy-efficient manner (LePhan and Yoshino 2010). The connection between designand the escalation of energy consumption for cooling has beenshown to be significant, especially when considering the ef-fects of urbanisation and rising urban temperatures (Nam et al.2015). The increasing use of AC combined with global trendsin urban and building design enforces a growing urban heatvulnerability as well as increased emission of greenhousegases.

Socioeconomic challenges

At present, AC is mainly an investment made by individualsand enterprises. Its costs comprise the initial investment,maintenance, and running electricity expenditures. In a house-hold context, AC is generally a local solution addressing the

heat problem in one room at a time, which in practice meansthat a house or apartment without a central cooling systemneeds several AC systems to be able to cool the whole livingarea. Central cooling systems exist and are mainly used inoffice buildings or in the upper range private homes. As theeconomic burden to install a cooling system lies on the indi-vidual household, it is causing heat inequities between richerand poorer segments of society. O’Neill (2003) has shown thatimprovements of social conditions can reduce the inequalitiesof heat mortality.

With the improvement of living standards, electrical house-hold appliances become more popular and the household en-ergy consumption increases (Le Phan and Yoshino 2010).This situation can be illustrated by the case of Hanoi, whereLe Phan and Yoshino (2010) show that the number and fre-quency of use of AC units are related to the households’monthly income and have greater effects on the annual energyconsumption than the use of any other household appliance.The electricity consumption of households using ACwas 4 GJhigher than of those without (Le Phan and Yoshino 2010).This illustrates that the improvement of living conditions re-sults in lifestyle changes, such as increased AC dependencyand thus increased energy consumption. For a high-incomefamily, the investment in one or two AC systems or a centralcooling system and the payment of the electricity bill are lesserproblems. For a poorer family, buying an AC and paying forthe electricity may be impossible.

In addition to economic inequality, there is also a genderaspect to AC use. In Hanoi, for example, AC systems arerarely used in the kitchen where it is particularly warm fromcooking activities (Phan and Yoshino 2010). There are alsoother studies showing gender biases related to the adoption ofnew technology (e.g. Gasper and van Staveren (2003), Iversen(2003), and Fernandez et al. (2013)). Moreover, males andfemales do not spend an equal amount of time in each roomof the house, and women generally are more engaged in do-mestic activities than men (Carswell 2012) and spend moretime at home. The location of the AC units may, in otherwords, strengthen inequality both within and betweenfamilies.

Furthermore, urban residents, especially the urban poor, arevulnerable to heat waves due to sub-standard housing, such aspoor roofing and less green surroundings (Harlan et al. 2006).Evidence also indicates that the poorest, often living andworking in the urban core, are more susceptible to UHI effects(O’Neill 2003). Hence, being unable to afford the purchase orrunning costs of AC causes several inequities and humanrights challenges including social, economic, and gender-related inequalities.

Moreover, the poorer segments of society are less likely towork in an AC environment, which in a hotter climate exposesthis societal group to more heat. Several studies show howheat exposure impacts workers in India (Venugopal et al.

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2016; Lundgren et al. 2014; Balakrishnan et al. 2010;Ayyappan et al. 2009). The workplaces studied byVenugopal et al. (2016) had very high heat exposure in thehot season, often reaching the international standard safe workvalues (ISO 7243:1989, see example in the next section)impacting worker’s health and productivity. AC is commonlynot used in these workplaces; however, due to the increasingadoption of AC (BIS Research 2015) together with the expect-ed increases in temperature as the result of climate change inthe region (IPCC 2013), further impacts on workers’ produc-tivity are expected in addition to adverse health impacts.

Biophysical challenges

The physiological basis for the effects of heat on humansis well understood (e.g. Burton (1937), Ladell (1955),Budd (1974), Hales and Richard (1987), and Parsons(2003)). Humans are born with a highly specialised com-plex of thermoregulatory sweat glands and a sensitivecontrol system. However, factors, such as pre-existing dis-ease, clothing, age, gender, heat acclimatisation ability,level of physical activity, and body size, can influencethis system. When the ambient temperature reaches orexceeds the human core temperature of 37 °C, there arewell-documented physiological effects on the humanbody, posing risks to some organ systems (Bennett andMcMichael 2010). As the core temperature begins to rise,skin blood flow increases and sweating is initiated. Atcore temperatures beyond 38–39 °C, there is an increasedrisk of heat exhaustion and beyond these temperatures,heat stroke can occur with a consequent failure of thethermoregulatory system (Jay and Kenny 2010). Healthconsequences range from dehydration, injuries, and heatfatigue to a higher burden of respiratory and cardiovascu-lar diseases, kidney failure, weakening of the immunesystem, and finally death (Parsons 2003).

One way of measuring heat is by using one of the heatstress indices. The importance of these indices is that theheat stress experienced is related to many environmentalfactors. One of these indices is the Wet Bulb GlobeTemperature (WBGT) widely used in assessments of oc-cupational heat stress (Bernard et al. 2005; Gao et al.2017 this issue). The ISO standard for WBGT (ISO7243:1989) incorporates environmental temperature, hu-midity, and solar radiation (Kleim et al. 2002; Gao et al.2017 this issue). A WBGT of 27 °C is seen as a thresholdfor the need for actions to protect workers, depending onthe intensity of the work and clothing worn (ISO 1989).Assuming that the indoor temperature is similar to out-door temperatures without AC, the contribution of solarradiation to WBGT needs to be discounted. Using Hanoias an example for a future potential heat exposures inresidential buildings, Fig. 2 shows such an average

calculated WBGT heat stress index for the month ofMay in Hanoi over time based on the IPCC’s representa-tive concentration pathway (RCP) of 8.5 (Climate CHIP2016; IPCC 2013) using modelling data from theUniversity of East Anglia. All simulations reach thethreshold WBGTs of 27 °C or more before 2050, evenwithout the contribution of the UHI effect. This indicatesa challenging future for Hanoi. It strongly suggests anincreased need to reduce indoor temperatures and if ACis the main available technology, it is likely to be increas-ingly used.

Humans are able to acclimatise to heat (Parsons 2003).Acclimatisation to a hot environment commonly occurs after7–14 days of at least 2 hours daily heat exposure (NIOSH2013). However, physiologically, it is possible for people tolose their heat acclimatisation when spending a majority oftheir time in AC environments, although the evidence is un-clear (Kovats and Hajat 2008). A substantial amount of timespent indoors is required to lose heat acclimatisation (Garrettet al. 2009). Generally, acclimatisation effects are consideredto be lost if the heat load has not been experienced for over2 weeks. Re-acclimatisation depends on individual factors andthe extent of time unexposed to heat (Ashley et al. 2015;Cheung and McLellan 1998; Pandolf 1998). Several scholarspoint out that more research is needed concerning acclimati-sation (Pandolf 1998; Aoyagi et al. 1997; Garrett et al. 2009;Lim et al. 1997; Gill et al. 2001; Weller et al. 2007; Wyndhamand Jacobs 1957).

Behavioural challenges

Culturally, AC has brought with it what can be called an en-capsulation of the home in warm regions and has led to sig-nificant changes in the social geography of the home, as wellas the neighbourhood (Wilhite 2009). The adoption of AC isglobalised and is occurring at a rapid pace, fostered by thespread of modern building practices and faith in modern tech-nical solutions to achieve indoor thermal comfort. Localknowledge about how to develop a comfortable climate, bothindoor and in the neighbourhood, is lost in this process andcooling solutions are increasingly left to technical experts(Wilhite 2009). Wilhite (2009) goes on to argue that the cur-rent high demand for AC is socially and technically construct-ed, originating in the USA, and a part of the global discourseof how a modern house should be built—a developmentfavoured by powerful commercial actors.

Some researchers argue that with increased AC use, peopleare becoming both physically and mentally dependent andaccustomed to cooling, making them more vulnerable to in-creased urban heat (Nicol and Roaf 2012). As a consequence,traditional vernacular building styles found comfortable bypast generations cannot meet current thermal comfort stan-dards (Nicol and Roaf 2012). Moreover, de Dear and Brager

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(2002) argue that households living year-round with AC arelikely to develop high expectations for a cool environment andbecome dependent on thermal homogeneity within a narrowrange of temperatures. Brager et al. (2015) even suggest thatas people gradually become reliant on cooling, they will be-come liable to over-cooling.

Due to a global discourse on the ideal human body, there isalso an increasing fixation on eliminating sweat and body odour(Wilhite 2009). Humphreys et al. (2007) discuss a growing glob-al lifestyle and global fashion industry promoting clothing/dresscodes that are not in linewith global indoor climate requirements,including no sweating (Humphreys et al. 2007). The literature inthis research field thus suggests that the globalised perceptions ofa modern life is encouraging an increased use of AC.Behavioural and cultural mechanisms are still of dominant im-portance for daily survival in hot environments (Lundgren et al.2013), which makes changing individual norms and attitudesvital factors in the escalating demand for cooling technology.

Alternative or supplementary solutions to airconditioning

This section of the literature review focuses on alternative orsupplementary solutions to AC use. The section is structured inthree broad categories: climate-sensitive urban planning and

building design, alternative cooling technologies, and climate-sensitive attitudes and behaviours.

Climate-sensitive urban planning and building design

Urban planning is important to address the effects of climatechange (UN-Habitat 2007). An unfavourable outdoor and indoorclimate can be prevented or mitigated through the application ofclimate-sensitive urban and building design, which refers tomea-sures that adapt the urban landscape to the site, the region, andthe climate (Keitsch 2012). With appropriate urban design, theurban microclimate can be improved and the UHI effect consid-erably reduced. Urban morphology, in particular the height-to-width ratio of urban street canyons, has a significant influence onair temperature, solar radiation, and wind speed (Johansson2006). In addition, the orientation of streets and buildings inrelation to the prevailing wind directions has a large impact onboth outdoor and indoor ventilation (Givoni 1992; Ng 2009). Acompact urban design results in considerably less radiation atstreet level and consequently lower daytime temperatures, whichreduces thermal stress compared to a dispersed urban design(Johansson and Emmanuel 2006; Yahia and Johansson 2013,2014). However, since buildings cannot provide shading at highsolar elevations (around noon), overhead shading—eitherthrough vegetation or shading devices—is crucial to creating agood microclimate (Emmanuel et al. 2007; Johansson et al.2013; Yahia and Johansson 2014). Climate-sensitive building

Fig. 2 Future heat stresssimulations during the month ofMay in Hanoi, without takingsolar radiation into account.Produced by HOTHAPS soft(Kjellstrom et al. 2013; Lemkeand Kjellström 2012). The differ-ent colours represent the differentclimate models’ datasets of RCP8.5 (red—HadGem, violet—NORES, blue—GFDL, green—IPCM, and brown—MIROC+)

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design also includes various strategies to maximise ventilationand to minimise solar heat gain, such as proper orientation of thebuilding, adequate design of windows, and use of shading de-vices and of reflective surface materials (Givoni 1998).

The amount of vegetation affects both air temperatures andradiation in the urban outdoors. In hot and humid climates, plen-tiful vegetation in the form of large urban parks and gardensreduces urban temperatures considerably (Jusuf et al. 2007;Yahia et al. 2017 this issue). Vegetation can provide multiplepositive functions at both building and urban scales, includinga reduction of energy use in buildings during cooling periods(Pérez et al. 2014) and improved storm water management(Susca et al. 2011). Street trees, pergolas, etc., are beneficial tocreate shade in the urban outdoors. A combination of horizontaland vertical green structures is highly recommended to enhancethe outdoor thermal environment (Yahia and Johansson 2014;Yahia et al. 2017 this issue). Such green structures have not beenconsidered as an urban feature in the current Hanoi master plan,which does not include enough green areas to mitigate the UHI(Trihamdani et al. 2014). Until the beginning of the 1990s, Hanoiwas known as a green citywith tree-lined streets and avenues anda good number of public parks, gardens, and small rivulets andlakes (Matsumuto and Almec 2015). During the constructionboom in the 1990s, many of the water surfaces were paved orbuilt over and urban green decreased significantly in the citycentre (JICA 2007). However, the NUAs have relatively highgreen space coverage. A UHI simulation study conducted in2012 (Nam et al. 2015) investigated the cooling effects of thegreen space network proposed in the Hanoi master plan. Thesimulated weather data included air temperature, relative humid-ity, wind speed, wind direction, solar radiation and air pressure.The results showed that high air temperature areas, with temper-ature of 40–41 °C in the summer, would expand substantially inthe planned NUAs. Simulated nocturnal air temperature wouldincrease by up to 3–4 °C and wind speed was weaker than overgreen spaces. The results also showed that the green strategiesproposed in the master plan were able to reduced night-time airtemperature within the green areas but could not be expected tocool all of the built areas (Nam et al. 2015). Finally, traditionalurban forms and building designs have proven to effectivelymanage local climate conditions in many countries. Therefore,sustainable and climate-sensitive design requires learning fromvernacular ways of building in combination with modern designsolutions and technology (Yahia 2014).

Alternative cooling technologies

At present, there is ongoing research and development of in-novative cooling technologies and strategies that could poten-tially lower energy consumption (Chua et al. 2013; Desideriet al. 2009; Ghazali et al. 2012). District cooling systems andrenewable energy AC are potential alternatives to convention-al AC (Gang et al. 2015). Examples of district cooling are

available, for instance in Singapore, but not very commonaround the world (Jusuf et al. 2007). Solar cooling and ab-sorption chillers (referring to any conditioning system usingpassive solar), solar thermal energy conversion, orphotovoltaic conversion, are new technologies which have ahigh potential to replace conventional cooling technologybased on electricity (ESTIF 2010). The advantage with solarcooling is that the energy production is renewable and alsolocal which is good for the regional energy supply and for theenergy user. Local energy production makes each region moreself-sustaining and resilient to power failures (Lundgren andKjellstrom 2013).

Novel cooling technologies also include personal cooling,such as cooling vests with phase change materials (Gao et al.2012). Such systems have potential to cool the person’s micro-environment. However, they are often expensive and thus notaccessible or seen as a priority by the poor. At an individuallevel, many people who cannot afford AC are using home-made cooling devices with a similar effect, but built withsimple and inexpensive materials, such as fans, ice, and foamboxes. In Hanoi, some of these types of solutions have beencommercialised to meet the demands of low-income house-holds. Although such systems are available for the less afflu-ent in society, they have their own environmental impact, asenergy and water is needed to produce ice.

Climate-sensitive attitudes and behaviour

Studies indicate that behavioural changes may be more effi-cient than physical changes when it comes to reducing energyconsumption (Vale and Vale 2009). Thus, a more sustainableurban development with less AC use and less energy con-sumption does not only require technical solutions or expertknowledge, but also the involvement of civil society (Larsenand Gunnarsson-Östling 2009). It requires efforts from urbancitizens to contribute with an adaptive use of the built envi-ronment and an adaptive lifestyle, which for instance couldmean staying in the shade, having a siesta during the hottesttime of the day, or using climate smart clothing.

Mechanical cooling—providing thermal comfort by creat-ing a steady, monotonous environment—has been proven notto be ideal in several cases (Brager et al. 2015). Instead, anadaptive environment with elements of individual control hasthe potential to provide a superior thermal environment, as it isadapted to the outside heat as well as to the person. Researchhas shown that when a cool stimulus is applied to a local bodypart (e.g. hand, head), it serves to reduce whole-body thermalstress (Zhang et al. 2010).

However, many parts of the paradigm of how to build andprovide thermal comfort need to change in order for an adap-tive environment to become a reality (Chappells and Shove2005). Several researchers suggest that by activelyscrutinising what is perceived as an ideal indoor environment

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and the associated ways of life, it is possible to develop anunderstanding of how we can design more sustainable futurehousing in different climatic conditions (Chappells and Shove2005). In addition, one has to keep in mind that thermal com-fort is individual and can only be understood through a per-spective that accounts for the context of historical, technical,and social change (Wilhite 2009).

Suggested solutions and responsibilityat different societal levels

In this final section, we relate the identified solutions to differ-ent societal levels. Solutions at the individual level includechanges in behaviour, awareness, the deployment of micro-cooling, and personal adaptive strategies. At the communitylevel, there are solutions that can help the most vulnerable,including shared cooled spaces, sharing work and other re-sponsibilities, and investing together in, for example, gardens,houses, and cooling technology. City authorities are responsi-ble for the development of urban space that can handle increas-ing urban heat, for developing initiatives, and for ensuring thatthe processes are participatory. The national level is responsi-ble for providing infrastructure (large-, medium-, and small-scale) along with initiatives such as subsidies for sustainablecooling solutions. In addition to these solutions, participationbetween the actors of one level and the collaboration of actors

between levels has been forwarded as being a central means tofacilitate learning and increase the implementation and dis-semination of new technologies as well as decrease vulnera-bility (Ahmad and Abu 2015; Bal et al. 2016). Participationcan be seen as a cross-cutting solution that is usually used incombination with one or two of the other solutions, either toenhance the uptake of a solution at one level or to create uptakeand learning between levels by creating a learning process.Table 1 provides an overview of alternative or supplementarysolutions on the different levels.

It is clear that AC has its advantages but if we chose tocompletely rely on it for cooling, it can lead us to a situationwith escalating energy consumption, heat stress inequalities,and uncontrollable chains of risks. To address these chal-lenges, a range of actions is required and there is no singlesolution to provide cooling in a sustainable way due to thecomplex nature of the problem.

From the analysis, it became clear that there are sev-eral challenges related to AC use and all need to beconsidered in order to gain a more holistic perspectivewhen considering AC adoption. However, the identifiedchallenges and suggested solutions are by no meansexhaustive and there is an urgent need for a betterand more holistic approach for how to handle our grow-ing urban heat challenge. Different parts and levels ofsociety need to cooperate and new ways of involvingcivil society must be developed.

Table 1 Suggested solutions through a division of measures and the societal levels responsible

Measures/level

Climate-sensitive buildingand urban planning

Alternative cooling technologies Climate-sensitive attitudes, behaviour,legislation, and education

Individual Double façade, cross ventilation,orientation of buildings,reflecting surface materials,shading devices,and roof and walls insulation.

Green roofs, green walls andshading trees.

Low-tech solutions including fans, self-inventedcooling systems using water, ice and fans, de-sert coolers (a simple mechanical ventilationsystem based on evaporative cooling), shadestructures.

High-tech solutions including solar panel-drivenAC, absorption chillers, small-scale electricityproduction (photovoltaic).

Awareness of the impact of heat and how to adaptto it by moving inside the house, climate smartclothing and food, footbath, work/rest regimes,wet towels, frequent showers, pouring of wateron roof and floor.

Community Common indoor and outdoorspacesto be used collectively on hotdays.

Shade structures.

Local electricity production (windmills,photovoltaic parks).

District cooling.

Help to the most vulnerable.Capacity building and risk management on

district level.

City Building orientation adjusted tosolar radiation and main winddirections.

Protection of existing vegetation,rivers, and lakes. Establishmentof new green areas and shadestructures.

Municipal infrastructure for renewable energy(windmills, photovoltaic parks).

District cooling systems and innovative coolingtechnologies such as solar panel-driven ACand absorption chillers.

Local laws and regulations for climate-sensitivedesign.

Capacity building for professionals and citizens.Risk assessment initiatives.

National Developing urban planningregulations to includeclimate-sensitive designand planning.

National infrastructure for renewable energysupply (large-, medium-, small-scale electricityproduction).

Capacity building on national level.Subsidies for climate smart solutions.Local laws and regulations for climate-sensitive

design.Systems for risk management.

408 Int J Biometeorol (2018) 62:401–412

A circular learning process between different levels in societyis necessary. Instead of leaving all the responsibility for handlingheat to the single citizen or household, the responsibility shouldbe more clearly shared. Here, the local and national authoritieshave to take the lead and at the same time promote engagementand suggestions from civil society. For example, to handle chal-lenges linked to culture and behaviour, civil society can play arole to foster climate-sensitive attitudes. Apart from the individ-ual’s choice to live in a more climate-sensitive way, the commu-nity can play an important role in the process of changing citi-zens’ attitudes and behaviour. Such communities include officialand unofficial unions, organisations, and local people. Accordingto Geertman and Le (2008), the involvement and participation ofcommunities also has a positive impact on households’ incomeand the living environment. This co-operation on the communitylevel could also be the basis for joint investments for coolingsystems or energy production. The challenges of unequal accessto AC are present and need to be tackled by looking at alternativesolutions and ensuring that either the community or the city levelis able to protect the more vulnerable segments of society.

When contemplating future directions of thermalcomfort, it is also important to reflect on historical waysof handling heat, as centuries of developing vernacularways of coping and adapting to heat are being lost in amatter of decades or even years. Behavioural and cul-tural mechanisms are important for everyday coping inhot environments, but the increased use of AC com-bined with global trends in urban and building designgenerates increased urban heat vulnerability as well asincreased emission of greenhouse gases.

Conclusions

The purpose of the research presented in this paper was toexplore the challenges linked to increased AC use, and todiscuss possible alternative or supplementary solutionsthat could be more sustainable based on a literature re-view. The results show that there are multiple challengesin relation to AC use that have to be considered. Thechallenges are not only related to an increase in energyconsumption and the associated adverse environmentaleffects, but to individuals and societies becoming moredependent on AC. This is because frequent use of ACcan lead to humans losing the capacity to handle heat bothphysically and mentally, and thus make them more vul-nerable to increasing urban heat. Moreover, increased heataffects people unequally as different socioeconomic seg-ments of society have different capacities for respondingto the escalating challenges.

This paper identified several measures to take intoconsideration to reduce the fast growth of AC use: theimplementation of more climate-sensitive building and

urban design, the development of more energy-efficientcooling devices that rely on renewable energy and arealso affordable for poor people, the promotion of achange towards more climate-sensitive life styles, andthe support of co-operative cooling solutions on com-munity and city levels that include active participationin the development of such structures by local commu-nities. In conclusion, there is a need for a more holisticview both when it comes to combining various solutionsas well as involving various levels in society.

Acknowledgements We are grateful to the Pufendorf Institute at LundUniversity for initiating and funding the HEAT Theme Project and all theresearchers involved.

Open Access This article is distributed under the terms of the CreativeCommons At t r ibut ion 4 .0 In te rna t ional License (h t tp : / /creativecommons.org/licenses/by/4.0/), which permits unrestricted use,distribution, and reproduction in any medium, provided you give appro-priate credit to the original author(s) and the source, provide a link to theCreative Commons license, and indicate if changes were made.

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